For a wide variety of applications, chairs and other types of seating furniture are nowadays provided with features which provide enhanced comfort to the person using the chair. For illustration, office-type chairs are commonly utilized in modern working environments to provide an occupant with a level of comfort while performing certain tasks that require a person to be in a seated position for an extended period of time. Similar features may be provided in other types of chairs to provide enhanced comfort to the person sitting on the chair.
One common configuration for such a chair includes a chair base assembly and a superstructure. The superstructure may include components which enable the user to recline or “tilt” the backrest of the chair. This basic chair configuration allows users to change their sitting position in the chair as desired, such that fatigue may be minimized during long sitting periods.
In recent years, chair designs have implemented a feature where the recline characteristic of a chair backrest may be altered. For illustration, the force applied by the chair backrest during a recline motion may be varied, so as to better accommodate the needs of different users. Adjusting elements may be provided on the chair which allow a user to manually adjust the force applied by the chair backrest. Alternatively or additionally, weight-responsive chairs may be provided with a mechanism in which the force applied by the chair backrest during a recline motion depends on a weight of a person sitting on a seat of the chair.
Such tilt mechanisms for weight-responsive seating furniture offer constructive simplicity and lend themselves to a cost-efficient production. However, despite these qualities conventional tilt mechanisms for weight responsive seating furniture may suffer from shortcomings. Such shortcomings may include one or several of knee rise, heel rise and/or shear effect and back compression. In the art, knee rise refers to the movement of the front end of the seat along an upward arc when the back is reclined. This movement causes the user's knees and thighs to rise. In the art, heel rise refers to the effect that the user's heels loose contact with ground as a result of the upward movement of the front of the seat. In the art, shear effect and back compression refer to the effect that, while reclining the backrest, the seat rises upward because of its connection to the back support and the user's back slips against the backrest of the chair while being raised. This last issue also causes a compression of the user's back, still because of the seat's rear portion being raised. There is a continued need in the art for weight-responsive tilt mechanisms which mitigate one or several of knee rise, heel rise and/or shear effect and back compression.